So, I've not been restarting my Mac Pro for at least a few weeks, because...well, why bother? But, I returned from a trip and the 10.6.7 upgrade was out, so I ran software update, restarted and... The memory configuration utility cheerfully informed me my RAM was in the suggested configuration. Odd I thought, since I hadn't changed it. Then when I went to System Profiler...I have 6 gigs of RAM. Except there's supposed to be 10. Slot 1 and 2 are occupied by 4 GB modules from OWC, and 3 and 4 are occupied by 2 of the stock 1 GB modules from Apple. Slot 1 is currently being reported by System Profiler as Empty. I booted from the Install CD to make sure it wasn't the new update - same thing, as it is in Windows 7. So...did I just have a RAM module fail?